I am not an expert on open cab pickups, but I do have a 29 phaeton and 28 roadster. I believe the sill plates for phaetons and roadsters (they are the same) would work on a OCPU. The subrails, I believe, are the same where the sill covers are located on phaetons/roadsters and OCPU's. The only concern is where the FORD script is located on the phaeton/roadster and the OCPU sill covers. I suspect they would be in the same location, as Ford probably used phaeton/roadster sill covers for OCPU's. I assume you have phaeton/roadster sill covers you want to use for the OCPU. Just line the sill covers up on your pickup and see if the Ford script would show or would be missing or partially missing when you cut the covers to fit your pickup.
Rusty Nelson